1. Field of the Invention
The present invention is directed to the field of circuitry for controlling the operation of bi-directional D.C. motors and more specifically to the area of such circuitry for use with power window drive motors in automotive vehicles.
2. Description of the Prior Art
Numerous prior art systems have been implemented to control the drive motors used to move windows between their fully closed and fully opened positions. In recent years, one-touch control systems have been found to be desirable, wherein a single, relatively short actuation of the control switch causes the drive motor to be continually energized. Even after the switch is returned to its unactuated position the motor is continually energized until the window reaches its fully closed or fully open condition.
In U.S. Pat. No. 4,001,661, a one-touch action type power window control system is disclosed in which the actuating control switch has conventional UP and DOWN actuating positions for conventional corresponding up/down control movement of the window. In addition, the actuation switch has two other positions designated as an "UP HOLD" and a "DOWN HOLD" position. Therefore, when the switch is actuated to an "UP HOLD" or a "DOWN HOLD" position, an appropriate relay is latched so as to continue to supply drive energy to the motor in the designated drive direction. A pick-up coil is used to sense the current flow through the motor and a circuit is connected thereto to determine when the the speed of motor rotation has dropped sufficiently to release of the latched relay.
The system in U.S. Pat. No. 4,373,149 utilizes separate flip/flop circuits connected to each side of a mechanical control switch so that actuation of the control switch to move a power window in a particular direction will cause the corresponding flip/flop circuit to assume a first state. Power to the window is thereafter continually supplied until the window is in its fully raised or lowered position, as appropriate, or until the control switch is again actuated.
In U.S. Pat. No. 4,476,416, a power window control circuit is shown, wherein the actuation switch provides for corresponding control of the motor drive circuit for short time periods corresponding to the actuation time of the switch, as long as such actuation time is below a defined first predetermined time period. If the actuation of the switch is continuously maintained for a period of time that exceeds the first predetermined time period but is less than a defined second predetermined time period, the circuit latches the motor drive. The circuit holds the latch continuously thereafter if the actuation switch is released before the expiration of the second predetermined time period. The motor is then stopped when the window reaches a predetermined position at the far end of its movement. If the actuation switch is held in one position continuously for a period of time that exceeds the second predetermined period of time, the latching circuit is deactivated so that subsequent release of the actuation switch will cause the motor to stop in its position at that particular time.